1. Field of the Invention
The present invention relates to an apparatus which is equipped with a battery compartment containing a battery and is supplied with electric power from the battery.
2. Description of the Related Art
Conventionally, primary or secondary batteries for small equipment are used widely for optical equipment such as cameras and video cameras; communications equipment such as portable phones and cordless phones; OA equipment such as notebook personal computers and electronic organizers; audio equipment such as headphone stereos, portable CD players, and cassette tape recorders; motor-driven equipment such as electric shavers and electric toothbrushes; toys; flashlight; etc.
Recent advances in portable equipment are remarkable, in which a significant role has been played by performance improvements of small batteries, especially development and improvements of small secondary batteries with high energy density such as nickel-cadmium, nickel hydrogen, and lithium ion batteries.
Voltage characteristics and discharge capacities which are important factors in evaluating battery performance will vary with the voltage and load used. In the case of small batteries, for example, when discharged continuously at a large current of nearly 1 A, secondary batteries such as nickel-cadmium, nickel hydrogen, and lithium ion batteries are capable of discharging stably at nearly their rated capacity, but alkaline manganese batteries can deliver only approximately 40 to 50% of their rated capacity and recover their capacity if they stop discharging for a while. On the other hand, when discharged continuously at a small current of nearly 0.1 A, even alkaline manganese batteries can deliver nearly their rated capacity and can discharge continuously for more than approximately 2.5 times longer than nickel hydrogen batteries and the like. Thus, still cameras, which are used for a shorter period each time and often left unused for longer periods than OA equipment or communications equipment, still have a high need for alkaline manganese batteries.
However, whereas the cylindrical nickel-cadmium battery, for example, has a structure in which a positive plate and negative plate separated by a separator and wound spirally are put in a battery case, the alkaline manganese battery has a structure in which a gelled negative electrode made of zinc powder and an electrolytic solution and positive electrode material made of manganese dioxide and graphite are separated by a separator and put in a steel container which combines a collector. Consequently, the contact resistance between the steel container and the positive electrode material increases with time, resulting in changes in battery characteristics.
One technique for dealing with this problem increases the surface roughness of the battery container to prevent changes in battery characteristics, i.e., the increases in contact resistance caused by nonuniform contact between a container surface and the active material, which results when the positive electrode material which is an active material expands after the battery is assembled (Patent Document 1).
It is believed that this technique can prevent expansion of the active material in the battery from causing changes in battery characteristics due to increase in contact resistance.
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-21359 (Paragraphs 0013 to 0016 and FIGS. 3 to 5)
However, apparent variations in battery characteristics can occur for other reasons, such as an unclean contact point between the positive armature of the apparatus which uses the battery and the positive electrode of the battery, variations in contact resistance caused by a concentrated electric current resulting from reduction in the effective contact area of a contact point, etc.
Thus, the disclosed technique alone cannot completely solve the problem of changes in battery characteristics in alkaline batteries and the like which result in insufficient discharge capacity rating.
FIG. 1 is a diagram showing a typical battery terminal used in a battery compartment of an apparatus.
In FIG. 1, a battery compartment 1 contains a positive armature 2 which is a U-shaped plate spring placed sideways and a negative armature 3 wound spirally. When, for example, an AA battery 5 is put in the battery compartment 1, it is pushed in with the negative side 6 of the AA battery 5 pressing against the negative armature 3 and with an electrode surface 7 of the positive electrode of the AA battery 5 rubbing against a contact point 2a of the positive armature 2. Meanwhile, the electrode surface 7 of the positive electrode is cleaned due to the elastic force of the positive armature 2 and if the AA battery 5 is secured by a surrounding wall 1a of the battery compartment 1 and the elastic forces of the positive armature 2 and negative armature 3, so are the contact positions between the electrodes and battery terminals.
However, the battery compartment has a clearance 1b to allow for battery size variations. Consequently, if the AA battery 5 retreats into the clearance 1b, the electrode surface 7 of the positive electrode of the AA battery 5 will not rub sufficiently against the contact point 2a of the positive armature 2. Thus, the desired cleaning effect cannot be achieved. Also, the AA battery 5 will move around in the battery compartment 1 due to the clearance 1b, causing the contact position between the positive/negative electrode and battery terminal to fluctuate, and thus, resulting in variations in contact resistance.
In view of the above circumstances, the present invention has an object to provide battery-operated portable apparatus and the like equipped with a battery terminal which ensure sufficient discharge capacity with reduced variations in contact resistance between electrodes of the batteries and electrode armatures of the apparatus.